Resistors



Dec. 27, 1955 M. cARuso RESISTORS Filed April 21, 1953 INVENTOR: 4/44/0m/s0 ATTORNEY:

United States Patent RESISTORS Mario Caruso, New Bedford, Mass.Application April 21, 1953, Serial No. 350,165 3 Claims. (Cl. 201-67)This invention relates to the method of producing an improved type ofelectric resistors and the article made by this method.

The art of electric resistors is quite complex, and there exist numerouspatents and voluminous literature covering various ways of manufacturingresistors of different types.

The present invention contemplates an improved method of producingmoisture-impervious, insulated electric resistors which not only haveall the requirements of a stable, efiicient and practical resistor, butin addition possess certain very important and advantageous featureslacking in heretofore produced resistor structures.

The prime object of the present invention is to employ a relativelysimple, inexpensive but very effective method of producing amoistureproof and insulated resistor structure by the formation of ajacket or envelope composed of easily manufacturable and readilyassemblable parts made from prefabricated standard stock material alwaysavailable in the open market, and by compacting within that envelope aresistance compound, which latter, in consequence of its composition andof the method employed, becomes intimately joined or united with theenvelope material.

A more specific object of this invention is the provision of a method ofproducing insulated, moisture-impervious resistors, and which methodcomprises preparing envelope-forming parts made from prefabricated stockmaterial, such as rods and tubing, and wherein the tubing is cut torequired length, to efi'ect tubular members of future envelopes, andwherein end covers for that tubular members are shaped from standardrods, and which end covers are provided with apertures for the receptionof prefabricated electrodes, and which method further comprisespositioning of the electrodes in a certain way relative the end coversto facilitate their movement within and in outward direction in respectto the future envelope or jacket of the resistor, compacting aresistance composition within the future envelope, the movement of theelectrodes being effected by the compacting procedure, and whichmovement of the electrodes causes them to become firmly imbedded andanchored within the compacted resistance compound, thereby precludingtheir bodily movement within the finished resistor structure andpreventing their disengagement in normal usage from said structure, andwhich method further includes the steps of heat-sealing with one anotherall of the elements of the envelope, fusing the end cover material aboutthe electrodes, heat-sealing them within these end covets, therebypreventing moisture from ever penetrating into the interior of theresistor jacket or envelope, thus preserving the resistance compoundcompacted Within the envelope and precluding its deterioration, wherebythe intended resistance value of the device remains constant duringextensive use, if not subjected to abuse, and which method includes thestep of effecting a firm union be tween the compacted resistancecompound and its en- .velope.

A further object of this invention is the provision of an electricresistor, the envelope of which is made of moistureproof dielectricthermoplastic material, and wherein the parts of the envelope areprefabricated and assembled and are heat-sealed with one another afterassembly, and wherein the electrodes for the resistor comprise wirestructures with broad heads projecting into the envelope, and whereinthe heads form conical shapes, the conical faces of which being directedtowards the closing elements of the envelope, and wherein the electrodebodies are heat-sealed within the end elements of the envelope, andwherein the resistance compound is firmly compacted within the envelopeso that it forms intimate contact and union with the interior of theenvelope body and with the heads of the electrodes, and wherein theelectrodes are firmly anchored within the compacted resistance compound,thus preventing their movement within and their disengagement from theresistor envelope in ordinary use.

in exemplifying the afore-indicated method, first the differentcomponents of the resistor structure are prepared. The envelopecomprises three parts, a cylindrical tubular member made fromthermoplastic tubing, preferably of a phenol base such as phenobaldehyderesin mixed with a suitable filler and lubricant. For closing the endsof the tube there are provided end covers made of the same or similarmaterial in the form of prefabricated rods. These end covers comprisedisc structures with hub-like central enlargements, which latter areadapted to project into the tube member. The periphery of the discstructures are preferably beveled and so are the peripheral faces of thehubs. These end covers are provided with central apertures for thereception of the electrodes, which latter are also prefabricated andconsist of wire structures having substantially enlarged termini in theform of conical heads, and which heads are so positioned within theenvelope that in the finished resistor structures the conical faces arein adjacency with the hub enlargements of the covers, while the fiatbases of the electrode cones face one another.

The resistor compound is made from the usual ingredients such as carbonblack, an inert filler and a thermoplastic binder, preferably of thephenol-aldehyde resin base, and which binder, when the compound issubjected to pressure and heat, will effect an intimate union of thecompound with the interior surface of the prefabricated jacket orenvelope of the resistor structure.

With all of the components of the future resistor structure ready, oneof the electrodes is passed through one of the end covers so that theconical end of its head faces the hub enlargement of the cover. Theelectrode is so positioned that its head is somewhat distanced from thehub. Now the beveled periphery of the cover is pressed into one end ofthe tubular member while the latter is held Within a heatable die, thecover being supported by a plunger movable within the die. Now theresistance compound in granulated or powder form is poured into the tubeand compacted therein to the desired density. During the compactingprocedure portions of the compound are first directed into the spacebetween the electrode head and the end cover, and as the compactingprocedure progresses, the electrode head is caused to move in thedirection towards the cover, whereby the conical surface of theelectrode head exerts outward pressure against the compound. Thisfunction of the conical head surface causes a firm anchoring of the headwithin the compound, and, as the compacting of the compound continues,the electrode movement progresses until the apex of its cone engages thehub enlargement of the cover, and the outward movement of the electrodeis stopped. Obviously the pressure exerted by the conical surface of theelectrode head against the trapped compound is very substantial, wherebyan intimate contact between the head and the compound is efiected.

When the tube of the envelope is substantially but not quite completelyfilled with the compressed compound, there is added loose compound abovethe tube. Now a second electrode is passed through the other end coverfor the tube and is held so that the electrode head extends a distancefrom the hub enlargement of the cover. .Now the cover is ready to beforced into the still open end of the tube under application of surplusloose compound which latter becomes firmly compacted by the forcibleinsertion of the second cover. The electrode of that cover firstpenetrates the already compacted resistance compound Within the tube,and the surplus of resistance compound at the top of the tube is trappedby the second cover as it is being inserted into the tube end and isforced against the already compacted compound. During that period thesecond electrode recedes toward the hub enlargement of the cover andcompresses the surrounding compound with its conical head portion as thebeveled edge of the cover enters the cylindrical interior of the tubeend. As the inward movementof the cover progresses, the compound incontact with the head is further compressed and more of the compound iscompressed by the end cover against the electrode head, whereby thelatter becomes firmly anchored.

During the aforedescribed procedure the die holding the tube is heated,and as the second cover is forced into the open tube end, the unusedsurplus of loose compound is removed by elevating the closed resistorstructure, whereupon the now closed resistor is caused to re-entcr theheated die and additional pressure is exerted against the end covers,and the resistor structure is subjected to greater heat. This added heatbrings about the fusing of the tube material with the cover material andcauses plasticizing or softening of the thermoplastic binder in thecompound. As a result a firm, intimate union between the compound andthe interior surfaces of the resistor envelope is effected, as well asthe sealing of the electrodes in the end covers for the tube; theresistor structure is thus finished and is removed from the die.

The above outline method will be more clearly understood by referring tothe accompanying drawings, where- Fig. l is a perspective view of afinished resistor produced by the aforesaid method;

Fig. 2is an enlarged cross section taken approximately along a planeindicated at 2-2 in Fig. 1;

Fig. 3 shows all the elements of the resistor with the exception of theresistance compound;

Fig. 4 is a vertical section through a heatable die hold ing the tubewith one attached end cover of a future resistor structure prior tocompacting resistance compound within the tube;

Fig. 5 shows a section similar to that of Fig. 4 with the compoundpartly compacted and with the second cover ready to be inserted into theother tube end;

Fig. 6 shows the electrode structure in its final closed position priorto the removal of unused surplus compound;

Fig. 7 shows the resistor in its elevated position with all surpluscompound removed;

Fig. 8 illustrates the resistor within the heated die to effect thefusing of the resistor elements and the sealing of the electrodes; and

Fig. 9 shows the finished resistor on its way to be discharged from thedie.

In Figs. 2 and 3 the components of the resistor are clearly illustrated.Numeral 10 denotes a cylindrical thermoplastic tube preferably made of aphenol base. This tube is cylindrical throughout including its interiorsurface. Adapted to engage the ends of the tube are covers 11 and 12,each comprising a stepped, disc-shaped structure having a peripheralbeveled surface 13, adapted for press fit with the tube ends, and ahub-like enlarge- 4 ment 14 also provided with a beveled peripheralface, and which end covers for the tube have central apertures 15 forthe reception of electrodes 16. These electrodes comprise wire shanks 17with relatively large heads 13 which are acutely cone-shaped, the apicesof their conical bodies being adapted to assume final positions adjacenthubs 14, while their flat bases are disposed opposite one another in thefinished product, as clearly observable from Fig. 2.

It will become presently evident from the detail description of themethod, that the beveled faces 13 of the end covers are forciblyinserted in the cylindrical ends of tube 10, whereby these tube ends aresomewhat deformed interiorly but are kept cylindrical exteriorly. Withinthe envelope or jacket formed by tube 1%} and the two end covers 11 and12 there is held a resistance cornpound 19 which is compacted to therequired density corresponding to the electric resistance requirement ofthe device.

In Figs. 4 to 9 there is illustrated a die 2% comprising a lowerstationary member 21 and an upper movable member 22. The lower member 21is either heatable or may be heated internally by high frequencycurrent. in the upper movable member 22 there is provided a funnelshapeddepression 23 with a cylindrical continuation 24.

At the beginning of the procedure of making the instant resistancestructure die member 22 rests against die member 21, as shown in Figs. 4and 5. Registering with cylindrical extension 24 of upper die member 22is a cylindrical passage 25 within member 21, and in which passage isoperatively mounted a plunger or piston 26 provided with a centralpassage 27 for the reception of the wire body of an electrode. In theposition of piston 26 shown in Fig. 4, the upper piston end supports oneend of dielectric cylinder 1t) and the outer face of end cover 11. Endcover 11 and tube 10 are partly assembled before they are placed intothe passage 25 of die 20. The preassembly of the two elements ispreceded by first inserting an electrode 16 into end cover 11 so thatthe wire portion thereof passes through aperture 15 provided in thatcover and so that head 18 is positioned a substantial distance away fromhub 14. Then the preassembled tube and end cover 11 are placed intopassage 25 so that cover 11 rests against the top of plunger 26,whereupon a second plunger 27, indicated in broken lines in Fig. 4, isforced against the upper end of tube 10, and causes the penetration ofend cover 11 into the lower tube end. Now plunger 27 is removed andsubstituted by a compound-compacting plunger 28 provided with aninterior bottom recess 29, adapted for clearing the inserted electrodehead. Plunger 27 is so dimensioned that it can pass through funnelextension 24 of upper die member 22 to engage the upper face of tubeIt), and plunger 28 has a diameter approximating the interior diameterof that tube.

In the diagram illustrated in Fig. 4 compound material 19' in powderedor granulated form is introduced through funnel 23 into the tube. Thesupply of loose compound into the funnel preferably continues as plunger28 repeatedly decends into and moves out from cylinder 16, to compactthe compound within the tube to its required density and to fill thelatter approximately That procedure can be modified in providing arelatively tall column of loose compound above tube 10 and a longerstroke for plunger 28, so that a single inward movement of the plungerwill compact the required amount of compound within the tube.

During the compacting procedure the loose particles of the compound aredriven by the circumferential face of the lower end of piston 28 abouthead 18 of the electrode, and toward end cover 11. At the same time head13 is caused to gradually move toward hub 14 until it is stopped whenthe head reaches that hub. During the downward movement of head 18 thecompacted com pound adjacent the conical head portion is very firmlycompressed and exerts pressure against cover 11 and the wall of cylinder10, whereby the head becomes firmly anchored within the compound.

When the tube is filled with the required amount of compacted compound,the following next step in the method comprises the introduction of endcover 12 into the upper tube end. First an electrode is passed throughthe cover so that its head 18 extends a distance from hub 14. A plunger30, provided with an interior passage 31 for accommodating the wire endof the electrode, now brings end cover 12 towards the upper tube end. Aswill be seen in Fig. the compacted compound within the tube terminatesalong line 32. It will be also observed from that figure that an amplesupply of loose compound is retained Within funnel 23 and itscylindrical extensions 24. As now plunger 30 moves toward the upper endof tube 10, head 18 of the electrode penetrates the central upwardlyextending portion of the compacted compound and forces that portiontowards the cylinder wall, While cover 12 presses additional compoundinto the cylinder. By the movement of cover 12 into the tube end thecompressed compound within the tube will stop further movement ofelectrode head 18, and at the same time compressed compound is forcedagainst the conical face of the head. At the time cover 12 first engagesthe inner edge of tube and as the cover progresses into the upper tubeportion, additional compression of the compound is effected. Thus theelectrode head becomes firmly anchored within the compound.

When plunger 30 reaches the position shown in Fig. 6, tube 10 is nowcompletely closed by the two covers 11 and 12 and heads 18 of theelectrodes assume their intended position adjacent the hubs of thecovers. At the position of the resistor shown in Fig. 6 the uppermovable member 22 of the die is lifted and surplus compound 19' formerlyheld in funnel 23 is permitted to gather upon the upper face of diemember 21 and about plunger 30. Now both plungers 26 and 30 are movedupwardly while holding tube 10 between them; at that position of thetube, shown in Fig. 7, all of the loose compound is removed from the dieby either suction or air pressure.

Now the plungers and the tube are moved back into the lower die member21 to the position shown in Fig. 8, at which position the resistancestructure is subjected to pressure from both ends by plungers 26 and 30and to sufficiently increased heat, supplied either by way of the die orby diathermically heating the resistor structure, to effect fusing ofthe tube material with the material of the end covers, to promotesealing of the electrodes in passages of the covers, and to plasticizethe thermoplastic binder of the compound so that the latter is caused tointimately contact or even fuse with the interior surface of theresistor envelope. Now the finished resistor is elevated and removedfrom the die as indicated in Fi 9.

lieferring again to Fig. 2, the fusing effects between tube 10 and endcovers 11 and 12 is exaggeratedly indicated at 33, as well as thesealing 34 of the electrodes within the cover apertures. In the finishedproduct, however, the fusing of the cover and tube materials and thesealing of the electrodes is not readily perceivable.

While the foregoing description appears to cover a rather slow-movingproduction process, actually all the operations involved are very rapidand extremely effective. Thus an ideal resistor structure is produced,which is impervious to moisture infiltration, securely protects andelectrically insulates the resistance material within the structure,thereby precluding variations or failure of the intended or desiredresistance value of the device. Due to its extreme simplicity andcompactness the resistor produced by the present method is very sturdy,withstands rough handling, endures easily the heat usually prevailing inelectronic devices, and resists even relatively high pressure whenapplied against its walls without changing its resistance value orotherwise deteriorating it.

In addition to the above advantages, the electrode construction andtheir secure anchorage within the resistor structure assures perfectcontact between the resistance compound and the electrodes and preventstheir disengagement from the ends of the resistor, except when extremeforce is applied. Tests conducted show that the wire ends of theelectrodes will break before the electrode heads can be pulled from thetube. That feature, in addition to the aforestated advantages, rendersthe resistor produced by the present method an invaluable, eificient andpractically indestructible element for the electronic field, and can bedepended on to retain unchanged its resistance value.

Obviously the density of the resistance compound and its compositiongoverns the resistance value of the future resistor. Resistancecompounds are well known in the art and need not be further explained.By the same token the degree of density of the compound within tube 10can be and had been determined by experiments and subsequent tests. Itseems evident therefore that resistors of any desired resistance valuesmay be readily produced by the present method Without any difiiculty.

Throughout the specification and the annexed claims the termthermoplastic is being employed to denote generally the type of materialused in both the prefabricated resistor envelope, that is the tubing andits end covers, as well as for the binder added to resistance compound,and it is to be understood that that term is meant to include also anyplastic materials known as thermosetting, that is substances whichbecome rigid by application of heat as they undergo a chemical reactionof polymerization. The aforesaid binder for the resistance compound, forinstance, can be thermosetting plastic, whereas the envelope material ispreferably made from thermoplastic substances.

While in the foregoing a specific structure of a resistor is describedas well as a specific method of producing the same, it is obvious thatthe drawings serve merely for explanatory purposes and that changes bothin the structure of the device and in the method of producing it aresubject to changes and improvements, such variations being deemed toreside within the broad scope of the present invention as defined in theannexed claims.

What is claimed as new is:

l. The method of producing a moistureproof, insulated resistor structurewhich consists of cutting to a desired length a cylindrical tube madefrom thermoplastic, dielectric material, providing end covers for saidtube also made from thermoplastic and dielectric material and havingbeveled outer edges, adapted for press fit engagement with the interiorend surface portions of the tube, each cover having a conical extensionadapted to project into the tube interior, each of said covers alsohaving a central aperture for receiving an electrode, providing wireelectrodes having at one of their ends a conical head or enlargement;inserting an electrode through the central aperture of one cover so thatits conical head projects a substantial distance from the futureinterior face of the cover extension, placing the tube into a heated dieand forcing a cover holding the electrode into one end of the tube,placing resistance compound, including a thermoplastic binder, into thetube while the latter is held within the heated die, supplying for andcompressing into the tube additional compound until it practically butnot completely fills the tube and moves the electrode head against itsend cover extension, retaining some of the compound above the filledtube, inserting an electrode into another end cover so that the conicalhead of the electrode extends a distance from the future inner face ofthat other end cover extension, moving the cover toward the other tubeend, thereby causing the head of its electrode to first partly penetrateinto the compressed compound with in the tube and then to move towardthe inner face of the cover extension, continuing the movement of thatother end cover, thereby additionally compressing and directing againstthe conical face of the electrode head and against the conus of itscover extension the now trapped, retained compound, forcing the bevelededge of that other end cover into the tube end, thereby causing theportions of the trapped compound located between the conical faces ofthe electrodes and the conical faces of the cover extensions to beforced against the interior wall face of the tube, thus effecting firmanchorage of the electrode heads within the resistance compound and anintimate contact between the electrode heads and the compound, removingthe surplus of that additional compound, compressing and heating the nowclosed tube within the die until the cover and tube material fuses andthe cover material seals the electrodes in the cover apertures, and thethermoplastic binder of the compound is plasticized and effects intimateunion between the compressed compound and the interior surfaces of thetube and covers.

2. In a moisturedmpervious electric resistor, a dielectric thermoplasticenvelope comprising a cylindrical tube filled with compressed resistancecompound and sealed at its ends by like-shaped dielectric, thermoplasticcovers having beveled peripheral edges and inwardly projecting hub-likeenlargements having beveled peripheral faces, electrodes havingrelatively thin-bodied portions which extend through the covers, saidelectrodes having relatively large acutely tapered conical heads, theapices of which abut the interior faces of the cover enlargements, saidbeveled peripheral cover edges engaging the interior end portion of thetube and being fused and heat-sealed with the latter, the thin-bodiedportions of said electrodes being fuse-sealed within the cover material;the acutely tapered conical surfaces of the heads serving not only tofirmly compress said resistance compound, but also causing the latter topress against the covers and the wall of the tube, whereby these headsare securely anchored within the compound so that they preventdisengagement of the electrodes from the resistor structure.

3. In a moisture-impervious electric resistor, an envelope or jacketformed from a dielectric, thermoplastic tube with forced-in dielectric,thermoplastic end covers, said tube being cylindrical, compressedresistance compound filling the tube, said end covers forming discs withhub-like, interior enlargements having beveled peripheral portions andcentral apertures, the annular faces of said discs being also beveled,electrodes comprising wire conductors having relatively large and broadacutely coneshaped heads, said wire conductors passing through and beingsealed within said apertures, the heads of the conductors projectinginto the tube interior with their apices adjacent said hub-like coverenlargements, the beveled faces of the cover discs forcibly engaging andbeing heatsealed within the interior end portions of the tube; thebeveled peripheral portions of said cover enlargements cooperating withthe acutely cone-shaped heads in that they trap and firmly compress theresistance compound between them and force the latter against the wallof the tube.

References Cited in the file of this patent UNITED STATES PATENTS2,244,548 Benkelman June 3, 1941 2,271,774 Megow et al. Feb. 3, 19422,282,398 Ehrlich May 12, 1942

